Generally, fine pattern formation is carried out by a photolithography method in manufacturing processes of a semiconductor device. A number of substrates called photomasks are normally used for such fine pattern formation. The photomask is generally such that a light-shielding fine pattern comprising a metal thin film or the like is provided on a transparent glass substrate. The photolithography method is used also in the manufacture of the photomask.
The photomask or an imprint mold serves as a master for transferring the same fine pattern in large numbers. The dimensional accuracy of the pattern formed on the photomask directly affects the dimensional accuracy of a fine pattern to be formed. In the case of the imprint mold, the sectional shape of the pattern also affects the shape of a fine pattern to be formed. With the improvement in integration degree of a semiconductor circuit, the dimension of a pattern is reduced and thus the photomask or the imprint mold is also required to have higher accuracy. Particularly, in the case of the imprint mold, since pattern transfer is carried out on the same scale, the required accuracy is equal to that of the pattern of the semiconductor circuit and therefore the imprint mold is required to have higher accuracy than the photomask. Likewise, a component having an optical function provided by a fine pattern such as grating is also required to have a pattern dimension and pattern accuracy less than a target wavelength and therefore the photomask or the imprint mold for the production of the optical component is also required to have a fine and high-accuracy pattern.
In the manufacture of a conventional photomask or imprint mold, use is made of a mask blank having a thin film of chromium or the like formed on a transparent substrate of quartz glass or the like and, after coating a resist on the mask blank, a resist pattern is formed using electron beam exposure or the like and, using this resist pattern as a mask, the thin film is etched to thereby form a thin film pattern (mask pattern).
In the imprint mold, in order to irradiate light in transfer, there is a case where a stepped pattern is formed on the transparent substrate using the thin film pattern as a mask. Also in this case, the pattern dimension and accuracy of the transparent substrate is directly affected by the dimension and accuracy of the thin film pattern.
For example, as a means for etching the thin film containing chromium, use is normally made of wet etching using diammonium cerium (IV) nitrate or dry etching using a mixed gas of a chlorine-based gas and oxygen.
There are conventionally known a method of forming a thin film pattern comprising a plurality of layers by the use of multi-stage etching, thereby improving nonuniformity in etching width and depth of the chromium film (see, e.g. Patent Document 1: JP-A-2005-530338), a method of forming a relatively thin film pattern using a resist pattern as a mask and further, using the formed thin film pattern as a mask, forming thin film patterns of second and subsequent layers, thereby enabling a reduction in thickness of the resist (see, e.g. Patent Document 2: JP-A-2006-78825), and so on.
On the other hand, for a magnetic disk for use as a hard disk or the like, use has conventionally been made of a technique of minimizing the width of a magnetic head and narrowing spaces between data tracks where information is to be recorded, thereby achieving an increase in density. However, the increase in density has reached the limit with the conventional technique and it has become difficult to ignore a magnetic influence and a thermal fluctuation phenomenon between the adjacent tracks. Recently, there has been proposed a new type medium called a discrete track type medium (Discrete Track Recording Medium; hereinafter referred to as a DTR medium) in which data tracks of a magnetic disk are formed so as to be magnetically isolated from each other.
The DTR medium is intended to improve the signal quality by removing (grooving) a magnetic material at portions unnecessary for recording. Further, after the grooving, grooves are filled with a nonmagnetic material, thereby realizing the angstrom-level surface flatness required for a magnetic disk drive. As one of the techniques for this fine-width grooving, the imprint technique is used.
Further, there has also been proposed a new type medium called a patterned medium (medium adapted to record a signal as a dot pattern) which has been developed from the DTR medium by further increasing the density. Also in pattern formation of this patterned medium, the imprint technique is considered promising.    Patent Document 1: JP-A-2005-530338    Patent Document 2: JP-A-2006-78825